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The Global ETD Search service is a free service for researchers
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Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 1 to 7 of 7 (0.346 seconds)| 1 |
Dynamic Response of a Rotor-air Bearing System Due to Base Induced Periodic MotionsNiu, Yaying 14 January 2010 (has links)
Oil-free microturbomachinery (MTM) are inevitably subjected to base or
foundation excitations: multiple periodic load excitations from internal combustion (IC)
engines in turbochargers, for example. Too large base excitations can produce severe
damage, even failure, due to hard collision or rubbing contact between a rotor and its
bearings. Therefore, it is paramount to evaluate the reliability of rotor-air bearing
systems to withstanding base load excitations.
In 2008, intermittent shock excitations, up to 30 g (pk-pk), were introduced to a
test rig consisting of a rotor (0.825 kg) supported on two hybrid flexure pivot tilting pad
gas bearings (FPTPBs). The experiments demonstrated the reliability of the gas
bearings to withstanding external transient load excitations. Presently, a shaker delivers
periodic load excitations to the base plate supporting the test rig. The whole system,
weighing 48 kg, is supported on two soft coil springs and its lowest natural frequency is
~5 Hz. The rod connecting the shaker to the base plate is not affixed rigidly to the test
rig base. The rod merely pushes on the base plate and hence the induced based motions
are intermittent with multiple impacts and frequencies. As with most practical
conditions, the base motion frequencies (5-12 Hz) are low respective to the operating
speed of the rotor-bearing system.
Rotor speed coast down tests evidence the rotor-bearing system natural frequency
when the gas bearings are supplied with feed pressures increasing from 2.36 to 5.08 bar
(ab). Shaker excitation induced rotor response, relative to the bearing housings,
contains the main input frequency (5-12 Hz) and its super harmonics; and because of
the intermittency of the base motions, it also excites the rotor-bearing system natural frequency, with smaller motion amplitudes than synchronous motion components.
The excitation of the system natural frequency does not mean rotordynamic instability.
With base induced motions, the rotor motion amplitude at the system natural
frequency increases as the gas bearing feed pressure decreases, as the rotor speed
increases, and as the shaker input excitation frequency increases (5-12 Hz). Hence, the
test rotor-air bearing system is highly sensitive to base motions, intermittent in character,
in particular when the gas bearings are supplied with a low feed pressure.
Predicted rotor motion responses obtained from XLTRC2 and an analytical
rigid rotor model, both including the (measured) periodic base motions, show good
correlation with the measurements.
The research results demonstrate further the applicability of gas bearings into oil-free
high speed MTM.
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The Experimental Testing of an Active Magnetic Bearing/Rotor System Undergoing Base ExcitationClements, Joshua Ryan 30 November 2000 (has links)
Active Magnetic Bearings (AMB) are a relatively recent innovation in bearing technology. Unlike conventional bearings, which rely on mechanical forces originating from fluid films or physical contact to support bearing loads, AMB systems utilize magnetic fields to levitate and support a shaft in an air-gap within the bearing stator. This design has many benefits over conventional bearings. The potential capabilities that AMB systems offer are allowing this new technology to be considered for use in state-of-the-art applications. For example, AMB systems are being considered for use in jet engines, submarine propulsion systems, energy storage flywheels, hybrid electric vehicles and a multitude of high performance space applications. Many of the benefits that AMB systems have over conventional bearings makes them ideal for use in these types of vehicular applications. However, these applications present a greater challenge to the AMB system designer because the AMB-rotor system may be subjected to external vibrations originating from the vehicle's motion and operation. Therefore these AMB systems must be designed to handle the aggregate vibration of both the internal rotor dynamic vibrations and the external vibrations that these applications will produce.
This paper will focus on the effects of direct base excitation to an AMB/rotor system because base excitation is highly possible to occur in vehicular applications. This type of excitation has been known to de-stabilize AMB/rotor systems therefore this aspect of AMB system operation needs to be examined. The goal of this research was to design, build and test a test rig that has the ability to excite an AMB system with large amplitude base excitation. Results obtained from this test rig will be compared to predictions obtained from linear models commonly used for AMB analysis and determine the limits of these models. / Master of Science
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Bilateral Control of Base-Excited Hydraulic Manipulators Operating under a Delayed and Lossy NetworkMaddahi, Yaser 15 January 2014 (has links)
Teleoperation of hydraulic manipulators is of potential when the presence of the operator, in a remote location, is inconvenient or dangerous. Augmenting such teleoperated systems using haptic sensation will further enhance performance, safety, and convenience. The advantage of using haptic force becomes more evident when it is employed to compensate for undesirable phenomena such as existence of a delayed and lossy communication channel or excitation of the manipulator base. The focus of this thesis is on haptic-enabled control of base-excited hydraulic manipulators that are controlled through a wireless communication channel. The targeted application is live transmission line maintenance.
Both unilateral and bilateral controls of teleoperated hydraulic manipulators are studied. On the unilateral front, position error is shown to be an important issue, especially when the position accuracy of the slave manipulator is violated due to fast motion of the operator’s hand at the master site, lack of responsiveness in actuation system, or poor quality of communication channel. With respect to bilateral control, three main challenges are identified, and solutions to these challenges are investigated: (i) accurate control of the slave manipulator when the communication channel is delayed and/or lossy, (ii) control of the teleoperated system when the slave manipulator is mounted atop a moving platform, and (iii) transparent force feedback to improve the position tracking of the system.
First, effects of network quality and slave manipulator base excitation are examined on performance of the teleoperated system. The position error between the haptic device implement and the hydraulic manipulator end-effector is shown to increase when the network is delayed and lossy. Next, excitation of the slave manipulator base deviates the end-effector from its reference trajectory, and the position error therefore becomes larger. To alleviate the position inaccuracy, a position referenced force feedback scheme is proposed. The scheme makes the input dynamics a better match with the slave dynamics. Combined with the virtual fixture force, the virtual fixture is shown to aid the operator in following a predefined virtual fixture trajectory. Due to complexity of dynamics, performance evaluations are mostly conducted using experimental validations on actual system in a laboratory setting.
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A Finite Element Modeling Study On The Seismic Response Of Cantilever Retaining WallsErtugrul, Ozgur Lutfi 01 September 2006 (has links) (PDF)
A numerical study was performed in order to investigate the effects of base excitation
characteristics (peak acceleration amplitude and frequency of the excitation), soil strength
and wall flexibility on the dynamic response of cantilever earth-retaining walls. In this
study, Plaxis v8.2 dynamic finite element code was used. Previous 1-g shake table tests
performed by Ç / ali& / #56256 / & / #56570 / an (1999) and Yunatç / i (2003) were used to compare the experimental
results with those obtained by finite element analysis. Comparison of experimental and
numerical results indicated that the code was capable of predicting the dynamic lateral
thrust values and bending moment profiles on the wall stems. In the light of these
validation studies, a parametric study was carried on for a configuration that consists of an
8 meters high retaining wall supporting the same height of dry cohesionless backfill. Total
and incremental dynamic thrust values, points of application and dimensionless bending
moment values were presented together with the results obtained from commonly used
pseudo static Mononobe-Okabe method and Steedman-Zeng approaches. According to
the finite element analyses results, total dynamic active thrust act at approximately 0.30H
above wall base. Base motion frequency becomes an important factor on magnitudes of
dynamic active thrust when it approaches to the natural frequency of the system.
Significantly high overturning moments were predicted at wall base in this case. It was
observed that increasing wall rigidity causes an increase in forces acting on the wall stem during
dynamic motion.
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[en] PENDULUM SYSTEM FOR THE PASSIVE CONTROL OF THE VIBRATIONS OF STRUCTURES UNDER BASE EXCITATION / [pt] SISTEMA PENDULAR PARA CONTROLE PASSIVO DAS VIBRAÇÕES DE ESTRUTURAS SOB EXCITAÇÃO DE BASE19 November 2021 (has links)
[pt] O controle passivo de vibrações em edifícios usando absorsores pendulares tem sido bastante estudado na literatura técnica e usado na pratica em edifícios altos como o Taipei-101 em Taiwan. Como a frequência do pêndulo depende apenas do seu comprimento e da aceleração da gravidade, para sintonizar a
frequência do pêndulo com a do edifício, tem-se como única variável de projeto o comprimento do pêndulo. Entretanto, em muitos casos, o comprimento necessário e o espaço requerido não se coadunam com o projeto. Nestes casos pode-se substituir o pêndulo clássico por um sistema pendular equivalente
composto por uma massa que se movimenta sobre uma superfície curva, permitindo maior flexibilidade no projeto do absorsor, já que o comprimento do pêndulo torna-se irrelevante e a forma da superfície curva pode ser otimizada. Em virtude do movimento da massa sobre a superfície curva, novas forças de
inércia e amortecimento não encontradas no pêndulo clássico podem aparecer. No presente trabalho um sistema pendular composto de uma massa que se desloca através de suportes rolantes sobre uma superfície curva é proposto para controle das oscilações de estruturas sob excitação de base. Este sistema
pendular tem a vantagem de poder ser usado tanto como um amortecedor pendular de massa sintonizada (APMS) quanto como isolador de base pendular (IBP). Como o sistema pendular pode, em certos casos, apresentar grandes rotações, barreiras que limitam o movimento são propostas, gerando forças de
impacto cuja eficiência no controle de vibrações é aqui investigada. / [en] The passive vibration control of buildings using pendulum absorber has been extensively studied in the technical literature and used in high buildings such as the Taipei-101 in Taiwan. Since the frequency of the pendulum depends only on its length and the acceleration of gravity, to tune the frequency of the
pendulum to that of the building, its length is the sole design variable. However, in many cases, the pendulum length and the space required for its installation are not consistent with the design. In these cases one can replace the classic pendulum with an equivalent pendulum system comprising a mass that moves on a curved surface, allowing greater flexibility in the absorber design as the length
of pendulum becomes irrelevant and the shape of the curved surface can be optimized. Because of the mass movement on the curved surface, new inertia and stiffness forces not found in the classic pendulum may appear. In the present work a pendulum system comprising a mass that moves through rolling bearings on a curved surface is proposed for control of the oscillations of structures under base excitation. This pendulum system has the advantage of being used both as a pendulum tuned mass damper (APMS) and as a base isolation pendulum system (IBP). As the pendulum system can, in certain cases, display large rotations, barriers which limit its movement are proposed, generating impact forces whose
efficiency in vibration control is here investigated.
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Linear Dynamic System Analyses with Creo Simulate – Theory & Application Examples, Capabilities, Limitations – / Lineare dynamische Systemanalysen mit Creo Simulate – Theorie & Anwendungsbeispiele, Programmfähigkeiten und Grenzen –Jakel, Roland 07 June 2017 (has links) (PDF)
1. Einführung in die Theorie dynamischer Analysen mit Creo Simulate
2. Modalanalysen (Standard und mit Vorspannung)
3. Dynamische Analysen einschließlich Klassifizierung der Analysen; einige einfache Beispiele für eigene Studien (eine Welle unter Unwuchtanregung und ein Ein-Massen-Schwinger) sowie etliche Beispiele größerer dynamischer Systemmodelle aus unterschiedlichsten Anwendungsbereichen
4. Feedback an den Softwareentwickler PTC (Verbesserungsvorschläge und Softwarefehler)
5. Referenzen / 1. Introduction to dynamic analysis theory in Creo Simulate
2. Modal analysis (standard and with prestress)
3. Dynamic analysis, including analysis classification, some simple examples for own self-studies (shaft under unbalance excitation and a one-mass-oscillator) and several real-world examples of bigger dynamic systems
4. Feedback to the software developer PTC (enhancement requests and code issues)
5. References
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Linear Dynamic System Analyses with Creo Simulate – Theory & Application Examples, Capabilities, Limitations –: Linear Dynamic System Analyses with Creo Simulate– Theory & Application Examples, Capabilities, Limitations –Jakel, Roland 07 June 2017 (has links)
1. Einführung in die Theorie dynamischer Analysen mit Creo Simulate
2. Modalanalysen (Standard und mit Vorspannung)
3. Dynamische Analysen einschließlich Klassifizierung der Analysen; einige einfache Beispiele für eigene Studien (eine Welle unter Unwuchtanregung und ein Ein-Massen-Schwinger) sowie etliche Beispiele größerer dynamischer Systemmodelle aus unterschiedlichsten Anwendungsbereichen
4. Feedback an den Softwareentwickler PTC (Verbesserungsvorschläge und Softwarefehler)
5. Referenzen / 1. Introduction to dynamic analysis theory in Creo Simulate
2. Modal analysis (standard and with prestress)
3. Dynamic analysis, including analysis classification, some simple examples for own self-studies (shaft under unbalance excitation and a one-mass-oscillator) and several real-world examples of bigger dynamic systems
4. Feedback to the software developer PTC (enhancement requests and code issues)
5. References
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